1. Field of the Invention
The invention relates to a process of forming a process of forming a HA/ZrO2 complex coating on a metallic surface, and more particular, to a process of forming a HA/ZrO2 bio-ceramic coating on a Co—Cr—Mo alloy by electrolytic deposition.
2. Description of the Related Art
An artificial articulation coxa includes a femoral stem, a femoral head and an acetabular cup. The major movement of the articulation coxa occurs between the femoral head and the acetabular cup. Therefore, corrosion made by the relative movement of the femoral head and the acetabular cup greatly affects the service life of the artificial articulation coxa. Co—Cr—Mo alloy is well used as the material of the articulation coxa due to its advantages of high mechanical strength and good toughness. However, the Co—Cr—Mo alloy is easily corroded to release toxic ions if stayed in human's body fluid for a long time. This problem can be solved by various surface modifications including hot isostatic pressing, plasma or flame spraying, ion-beam sputtering deposition, elelctrophoretic deposition, sol-gel deposition and radio-frequency magnetron sputtering.
ZrO2 is a ceramic material with high corrosion resistance, chemical stability and bio-compatible ability. One of the surface modifications utilizes the characteristic of ZrO2 to inhibit toxic ion release from the Co—Cr—Mo alloy and to prevent the corrosion of the Co—Cr—Mo alloy. For example, TW patent No. 138232 discloses ZrO2 has good adhesion to the Co—Cr—Mo alloy, and the ZrO2-coated Co—Cr—Mo alloy has very good corrosion resistance.
The bioactivity and bio-compatibility of Ca10(PO4)6(OH)2 (HA) has been proved. However, applications of the HA are limited due to its disadvantageously poor mechanical. At present, the HA is clinically applied to only non-load-bearing area. If the mechanical strength of HA can be improved, its applications must to be greatly extended, such as in use as the artificial articulation coxa.
The inventors have found that the combination of ZrO2 and HA increases the bioactivity of Co—Cr—Mo alloy as well as the mechanical strength and adhesion of HA, to improve the performance of the artificial coxa.
Furthermore, the ZrO2 and HA have to be sintered at a temperature higher than 500° C., which requires high thermal budget. High-temperature sintering always results in phase change of final products, for example, the hetero-phase of the obtained coating, such as DCP or β-TCP.
Therefore, there is a need of a high-quality surface modification on the Co—Cr—Mo alloy with low thermal budget, and of a highly surface modified Co—Cr—Mo alloy.